H. F. Mollet1*, G. Cliff2, H. L. Pratt3 Jr., J. D. Stevens4
1) Monterey Bay Aquarium, 886 Cannery Row, Monterey, CA 93940, USA
2) Natal Sharks Board, Private Bag 2, Umhlanga Rocks 4320, South Africa
3) NOAA/NMFS, Narragansett Lab, 28 Tarzwell Drive, Narragansett RI 02882, USA
4) CSIRO Marine Research, P. O. Box 1538, Hobart, Tasmania 7001, Australia
*Author for correspondence: mollet@mbay.net
Reproductive data from 95 mature female shortfin mako sharks Isurus oxyrinchus Rafinesque, 1810, including 35 pregnant females, together with data on about 450 post-natal fish were collected from around the world. Size at birth was approximately 70 cm total length (TL) and litter size varied from 4 to 25, increasing with maternal size. Embryo length-at-capture data predicted a gestation period of 15-18 months and late winter to mid-spring parturition in both hemispheres. A temporal analysis of uterus width index and gonadosomatic index of pregnant and post-partum females indicated that the reproductive cycle is three years. The median TL-at-maturity of females from the western North Atlantic (2.98 m) was larger than that of females from the Southern Hemisphere (2.73 m) and they were 16-19% heavier in the TL range of 2.5-3.5 m.
Recently ovulated females and a litter with 2.6-3.3 cm TL embryos having external gills, large yolk-sac, and still inside the eggcases, are described. We illustrate a 52.0 cm TL litter of embryos with huge yolk-filled stomachs. The embryos of 59.9 and 68.8 cm TL litters showed a decline in the mass of the yolk-filled stomach from 29.1 to 10.9% of total mass and increasing hepatosomatic indices from 3.7 to 7.0% as gestation advances. When the mass of the yolk-filled stomach was excluded, the mass-length relationship of shortfin mako embryos could be fitted with a power regression, similar to that of post-natal fish. The condition factor of lamnid embryos (including yolk-stomach mass) reached a maximum between 20-35 kg m-3 when the embryos are mid-term and have the largest yolk-stomachs. The condition factor of alopiid embryos remained constant, indicating that no large yolk-filled stomach develops.
Abstract of paper in Fishery Bulletin 98:299-318 (2000).